Little Blair Valley
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Little Blair Valley clear sky chart from 2005-11-05 to 2018-02-22.

This page is a summary of past forecasts. Even though it's based only on forecasts, some people use these pages as clue to a site's climate. But climate data based on actual observation should be preferred (if you can find it!).

Cloud, Transparency and Seeing forecasts are summarized individually. But because good observing conditions require a combination of minimum cloud cover, transparency and seeing, the individual forecast summaries can be difficult to interpret. The observing conditions section counts the combinations of conditions needed for common types of astronomical observation.

Observing Conditions

The following tables count the occurrence of the combinations of forecast and darkness conditions needed for different observations. Conditions are rated by by what percentage of the hours the observation would likely be attempted are usable.
Observation TypeMinimum conditions for hour to be usableOut of hours
Clear of CloudsTransparencySeeingSky Brightness
Planetary:50%(no limit)Average(no limit)Nighttime Hours
Deep Sky:70%Average(no limit)5.9Nighttime Hours
CCD Imaging:70%Below AveragePoor(no limit)Nighttime Hours

Percentages are of nighttime hours per month, or per year, when a particular observing conditions was met. Deep Sky percentages never exceed 50% because the moon is up half the time. Deep sky percentages are much lower for charts at high latitudes because of fewer dark hours in the summer.

Overall

PlanetaryData
Pts
Deep Sky
Max 60%
Data
Pts
Both Planetary and Deep Sky
Max 60%
Data
Pts
Either Planetary or Deep SkyData
Pts
CCD ImagingData
Pts
Night
65%
16810
40%
48916
28%
16766
76%
16766
62%
21251

By Month

MonthDays of MonthPlanetaryData
Pts
Deep Sky
Max 60%
Data
Pts
Both Planetary and Deep Sky
Max 60%
Data
Pts
Either Planetary or Deep SkyData
Pts
CCD ImagingData
Pts
January1st to 15thNight
65%
777
35%
2522
30%
776
75%
776
47%
1165
January16th to endNight
61%
832
41%
2522
31%
832
74%
832
49%
1195
February1st to 15thNight
63%
760
40%
2285
30%
757
78%
757
54%
1034
February16th to endNight
50%
660
39%
1979
28%
660
67%
660
45%
950
March1st to 15thNight
53%
720
38%
2139
28%
720
70%
720
57%
929
March16th to endNight
53%
768
38%
2076
22%
768
68%
768
58%
957
April1st to 15thNight
41%
719
40%
1799
13%
719
58%
719
56%
866
April16th to endNight
46%
720
44%
1800
14%
720
64%
720
66%
805
May1st to 15thNight
50%
554
42%
1634
21%
554
64%
554
68%
636
May16th to endNight
46%
562
42%
1685
19%
561
62%
561
68%
634
June1st to 15thNight
52%
540
38%
1620
22%
540
64%
540
78%
598
June16th to endNight
64%
540
39%
1620
27%
540
71%
540
83%
597
July1st to 15thNight
82%
510
31%
1530
25%
510
85%
510
68%
646
July16th to endNight
81%
591
36%
1618
27%
556
83%
556
63%
728
August1st to 15thNight
86%
717
38%
1790
23%
713
88%
713
78%
815
August16th to endNight
89%
764
44%
1910
30%
764
90%
764
73%
904
September1st to 15thNight
84%
720
40%
1894
28%
720
89%
720
75%
849
September16th to endNight
79%
716
50%
1980
40%
716
88%
716
81%
787
October1st to 15thNight
66%
720
45%
1980
30%
720
80%
720
69%
849
October16th to endNight
75%
768
49%
2289
42%
768
86%
768
74%
891
November1st to 15thNight
73%
760
38%
2470
35%
760
83%
760
61%
992
November16th to endNight
71%
780
43%
2535
40%
780
81%
780
59%
1041
December1st to 15thNight
65%
780
37%
2535
34%
780
74%
780
51%
1128
December16th to endNight
59%
832
38%
2704
32%
832
71%
832
46%
1255

Individual Forecasts

The length of each colored bar in the "occurrence of each Forecast" column is proportional to the number of times the chart forecast that color. The percentages are of the total number of hours per month, or per year, with a particular forecast. The colors as the same as those used in clear sky charts.

Note: Transparency probabilities are only counted for those hours that have 30% or less cloud cover. Seeing probabilities are only counted for those hours that have 80% or less cloud cover. If that's too tricky, try Observing Conditions instead.

Overall

Occurrence of each ForecastData
Points
Cloud CoverDay
111213346%73%
49325
Night
111212235%75%
49121
TransparencyDay
11%3412%26%40%
49023
Night
10%3413%27%40%
48924
SeeingDay
214%28%32%17%3
6412
Night
19%20%32%27%8%
16819

By Month

Percentage Cloud Cover SW (2006-)
Color Meanings:
Overcast 90% covered 80% covered 70% covered 60% covered 50% covered 40% covered 30% covered 20% covered 10% covered Clear
MonthDays in MonthOccurrence of each ForecastData
Points
January1st to 15thDay
2213413347%65%
1746
16th to endDay
321232345%8%63%
2051
February1st to 15thDay
2112213347%67%
1901
16th to endDay
1135%2446%9%59%
1641
March1st to 15thDay
2112113347%70%
1821
16th to endDay
1222445%5%70%
2145
April1st to 15thDay
112323346%71%
2149
16th to endDay
11145%81%
2160
May1st to 15thDay
11112135%80%
2316
16th to endDay
1122485%
2429
June1st to 15thDay
111112484%
2340
16th to endDay
1111288%
2340
July1st to 15thDay
2112212436%69%
2340
16th to endDay
121232346%8%64%
2437
August1st to 15thDay
1221334474%
2160
16th to endDay
21221235%6%71%
2292
September1st to 15thDay
111213336%73%
2064
16th to endDay
1111112284%
1980
October1st to 15thDay
11223479%
1980
16th to endDay
111232480%
1932
November1st to 15thDay
111213345%73%
1719
16th to endDay
112223446%70%
1755
December1st to 15thDay
222315%35%8%63%
1755
16th to endDay
211232335%8%63%
1872
January1st to 15thNight
1213323348%64%
2522
16th to endNight
3212213346%67%
2522
February1st to 15thNight
12224338%69%
2281
16th to endNight
134335%5%7%63%
1979
March1st to 15thNight
1111213348%70%
2139
16th to endNight
11111235%8%70%
2076
April1st to 15thNight
1221233476%
1799
16th to endNight
11113484%
1800
May1st to 15thNight
111325%82%
1634
16th to endNight
1112388%
1684
June1st to 15thNight
1111289%
1620
16th to endNight
11290%
1620
July1st to 15thNight
1212445%76%
1620
16th to endNight
1211212236%72%
1728
August1st to 15thNight
11223481%
1800
16th to endNight
11111123481%
1910
September1st to 15thNight
121223480%
1894
16th to endNight
111290%
1980
October1st to 15thNight
111123481%
1980
16th to endNight
1111235%81%
2289
November1st to 15thNight
11113335%75%
2470
16th to endNight
1111222245%74%
2535
December1st to 15thNight
223313447%66%
2535
16th to endNight
32232335%7%65%
2704

Transparency (when cloud cover <= 30%)
Color Meanings:
Too cloudy to forecast Poor Below Average Average Above average Transparent
MonthDays in MonthOccurrence of each ForecastData
Points
January1st to 15thDay
18%46%16%28%25%
1747
16th to endDay
18%36%18%27%24%
2051
February1st to 15thDay
14%35%15%30%30%
1901
16th to endDay
17%6%7%20%27%21%
1641
March1st to 15thDay
12%3316%32%31%
1821
16th to endDay
12%45%17%32%27%
2145
April1st to 15thDay
12%3412%41%25%
2149
16th to endDay
5%2316%34%37%
2160
May1st to 15thDay
7%2311%31%44%
2316
16th to endDay
41312%32%44%
2432
June1st to 15thDay
5%218%20%61%
2340
16th to endDay
5%11310%77%
2340
July1st to 15thDay
15%348%18%49%
2201
16th to endDay
16%5%7%17%25%27%
2284
August1st to 15thDay
13%339%24%46%
2146
16th to endDay
14%348%23%46%
2292
September1st to 15thDay
13%35%8%21%47%
2064
16th to endDay
7%12423%60%
1980
October1st to 15thDay
9%2210%28%46%
1980
16th to endDay
8%248%22%52%
1932
November1st to 15thDay
11%35%14%29%36%
1719
16th to endDay
12%45%14%26%37%
1755
December1st to 15thDay
17%5%5%19%22%29%
1755
16th to endDay
17%5%7%21%28%20%
1872
January1st to 15thNight
17%46%17%27%27%
2522
16th to endNight
16%45%19%22%31%
2522
February1st to 15thNight
13%45%15%27%33%
2292
16th to endNight
16%5%7%17%28%24%
1979
March1st to 15thNight
12%26%16%31%30%
2139
16th to endNight
10%36%17%32%29%
2076
April1st to 15thNight
10%25%15%38%26%
1799
16th to endNight
5%1313%35%40%
1800
May1st to 15thNight
5%1311%30%46%
1635
16th to endNight
5%119%36%45%
1685
June1st to 15thNight
49%22%61%
1620
16th to endNight
5%138%81%
1620
July1st to 15thNight
10%346%19%57%
1530
16th to endNight
13%27%15%28%33%
1618
August1st to 15thNight
7%2311%25%49%
1790
16th to endNight
9%227%23%53%
1910
September1st to 15thNight
7%238%23%53%
1894
16th to endNight
41327%62%
1980
October1st to 15thNight
6%3212%27%47%
1980
16th to endNight
6%1410%23%53%
2289
November1st to 15thNight
10%3311%34%37%
2470
16th to endNight
12%2314%31%36%
2535
December1st to 15thNight
15%46%18%26%29%
2535
16th to endNight
16%5%8%20%26%22%
2704

Seeing (when cloud cover <= 80%)
Color Meanings:
Too cloudy to forecast Bad 1/5 Poor 2/5 Average 3/5 Good 4/5 Excellent 5/5
MonthDays in MonthOccurrence of each ForecastData
Points
January1st to 15thDay
8%20%17%33%17%2
135
16th to endDay
421%27%29%13%3
323
February1st to 15thDay
316%29%35%11%3
326
16th to endDay
5%31%27%25%9%
264
March1st to 15thDay
422%33%24%12%1
270
16th to endDay
423%35%23%11%1
288
April1st to 15thDay
7%25%33%21%10%1
269
16th to endDay
327%34%24%8%2
270
May1st to 15thDay
223%36%26%7%2
288
16th to endDay
119%38%26%11%2
330
June1st to 15thDay
117%34%25%18%3
315
16th to endDay
1436%31%21%4
315
July1st to 15thDay
1224%42%24%4
305
16th to endDay
318%36%29%11%
327
August1st to 15thDay
1124%39%25%6%
315
16th to endDay
219%42%24%10%
332
September1st to 15thDay
2433%42%14%4
315
16th to endDay
210%26%42%15%2
315
October1st to 15thDay
115%32%35%14%
315
16th to endDay
112%22%30%28%4
246
November1st to 15thDay
213%20%35%24%4
135
16th to endDay
18%22%28%22%6%
135
December1st to 15thDay
12%17%42%25%1
135
16th to endDay
319%19%29%22%5%
144
January1st to 15thNight
29%16%32%28%10%
780
16th to endNight
5%9%19%31%27%6%
832
February1st to 15thNight
110%19%31%26%10%
764
16th to endNight
217%26%27%18%6%
660
March1st to 15thNight
214%26%28%22%4
720
16th to endNight
116%27%26%21%6%
768
April1st to 15thNight
121%32%22%15%4
719
16th to endNight
120%31%23%17%6%
720
May1st to 15thNight
14%33%32%16%2
555
16th to endNight
117%33%28%15%2
563
June1st to 15thNight
8%37%34%17%1
540
16th to endNight
1231%42%20%2
540
July1st to 15thNight
1111%47%33%4
510
16th to endNight
210%47%35%4
591
August1st to 15thNight
18%40%40%8%
717
16th to endNight
2430%49%11%
764
September1st to 15thNight
110%33%44%10%
720
16th to endNight
1413%32%36%11%
716
October1st to 15thNight
110%21%31%27%7%
720
16th to endNight
5%16%29%30%17%
768
November1st to 15thNight
6%16%35%30%11%
760
16th to endNight
27%16%26%31%16%
780
December1st to 15thNight
27%17%34%27%9%
780
16th to endNight
412%20%28%26%8%
832
Page generated at 2018-02-23 08:21:33. Version ac04

Copyright 2018 A. Danko


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